Molding of ceramic materials

ABSTRACT

A porous, open-pore, hardened, plastic composition suitable as a replacement for plaster for use as a mold in shaping a ceramic article by any of various ceramic shaping methods prepared by subjecting a water-in-oil emulsion to hardening, without breaking the emulsion, and then drying the hardened product, the emulsion having a viscosity of 1600-5000 cP and/or containing 2-12% by weight of an alkali-reactive, water-binding material, the water phase/oil phase ratio providing an open pore volume in the composition equivalent to 10-60% of the total volume of the composition.

This application is a division of application Ser. No. 054,682 filed May22, 1987 which, in turn, is a continuation of application Ser. No.764,851 filed Aug. 12, 1985 now abandoned.

For molding ceramic materials, plaster molds are used, to which varyingquantities of water are added in order to produce molds for casting,turning or press molding. Depending on the stress put on them, on thepore volume, on the surface quality and on the type of use, the moldscan be used from 50 to several hundred times. In addition to being aninexpensive material which is easily handled and versatile in its use asa mold for casting, turning or press molding, plaster has theadvantageous property that when in contact with pourable ceramiccompositions, it absorbs the water contained in the composition andthereby forms a body which requires approximately 1 to 30 minutes per mmof thickness and which separates from the form after further drying.

It is disadvantageous that the utility of plaster is limited, because ofthe limited number of times the mold can be used, and that the weight ofthe forms is heavy, which is a particular disadvantage in making largemolded articles. A further disadvantage is that the still-plastic bodyoften separates quickly from the mold. Possible replacements for plasteras a mold material have long been sought.

Only with die casting, in a method that has been known for about 20years--the body is formed in a closed mold by using slip under highpressure--was it possible to dispense with using plaster as a moldmaterial.

In order to produce die casting, turning and press molding molds, anumber of methods of producing molds made of porous solid materials areknown. For instance, water-soluble salts are admixed with hardenableresin molding compositions and after hardening of the composition, thesalts are dissolved out again; or plasticizable plastics, such aspolymethylmethacrylate or polyethylene, are pressed into a fine-grainedform under the influence of heat, similarly to how porous cast metalparts are produced by sintering fine-grained powder. In other methods,the porosity is attained by pressing inorganic, fine-grained powders,such as quartz, with a small amount of resin added as a binder. Finally,the use of molding compositions made from porous calcium silicatehydrate, which is mixed with coarse-grained plastic and hardened inautoclaves, has also been described. These methods have the disadvantagethat it is expensive and complicated to make the molds.

In German Pat. No. 19 28 026, a method has been published which forproducing porous solid materials recommends a hardenable,water-containing casting composition comprising fluid monomers that canbe emulsified with water and polymers in powder form which are insolublein water but which in the monomers are at least capable of swelling up;this composition is catalyzed and after being molded by casting ishardened. With the porous molds produced by this method, severalthousand unmoldings, in die casting, became possible, with the slip at apressure of 10 to 50 bar.

As indicated above, molds made by the known methods, especially whenthey were based on plastic, were heretofore suitable only to a verylimited extent for molding ceramic materials. Pressureless production ofa body from ceramic slip, which was typical for plaster, was impossible;it was not even considered attainable. Thus up to the present time,plaster remained virtually the only mold material used for moldingceramic materials in the field of casting, turning and press molding.

The object of the invention is to make the molding of ceramic materials,which is substantially bound to the use of plaster, more economical, toreduce the considerable expense for materials, and to replace theplaster with a molding material that, like plaster, has body-formingproperties, which is more resistant to stresses such as changes inmoisture content and in temperature, pressure and frictional wear, andwhich facilitates shaping the mold itself. In so doing, a further objectis that it be possible to use the same material as a mold for casting,turning, press molding and die casting, as well as to process plaster,in producing the working molds, in open or closed casting.

With the invention, further objects are that for casting processes, thewaiting times while full and the drying time should also be shortenedconsiderably; the number of successive, daily unmolding operationsshould be multiplied; it should be possible to regulate when the body isreleased from the mold; and the expense for energy and for molds shouldbe reduced to a minimum.

A further variant of the method is intended to replace and simplify thepreviously used die casting method, in which elevated pressures of 10-50bar are applied, by using a low-pressure method performed in accordancewith the invention, so that the expense for molds and machinery becomesvery low, and the mold waiting time becomes merely a fraction of that ofconventional casting methods.

According to the invention, mold parts comprising porous plastics areproduced from hardenable molding compositions containing water and areused for molding ceramic materials. These mold parts have an open porevolume, which is refillable with water, of at least 10% of the volume ofthe molding composition and have a capillary suction force, which whenthe mold wall is in contact with a fluid ceramic composition having ausual water content of approximately 25 to 35% by volume aspirates thesuspended solids and solidifies them, whereby, as when plaster is used,a body is formed that can be released from the mold within a time rangethat is adjustable depending on the mold material.

The filled waiting time and the drying time of the molded article, andhence the mold waiting time, are shortened considerably according to theinvention by incorporating additional compounds into the porous moldingcomposition comprising the mold, and by accelerating body formation andwater removal.

The speed with which a body is formed can be regulated to a desired timerange via the quantity of body formation accelerating additives that themolding composition contains. Varying the body formation, when themolding composition according to the invention is used, with and withoutbody formation accelerators, is shown in FIG. 1 as compared withplaster. The comparison in graph form, clearly shows the range ofadjustment, and in particular the superiority attained with the bodyformation accelerator, that is attained with the invention. Because ofthe rapid dewatering, the filled waiting times and drying times can bereduced to from 33 to 20% of the times required in conventional castingusing plaster molds.

An important component of the invention is the acceleration of the totalmold waiting time. This is attained by placing the slip located in theform under pressure, for example by means of a suitable fill level orwith the aid of compressed air. In contrast to the known die castingmethods, in which pressures between 10 and 50 bar are required, it issufficient in the novel low-pressure method to exert a pressure of 0.1to approximately 5 bar, depending on the body thickness and filledwaiting time desired, briefly upon the slip located in the mold.

With a slip intended for making bathroom fixtures, a body thickness of 4to 8 mm is obtained within 5 to 10 minutes at a slip pressure of only0.75 bar. The normal filled waiting time for these slips, in a plastermold, is 65-75 minutes, and the mold waiting time is 230 minutes. Withthe novel low-pressure method, mold waiting times between 12 and 15minutes, for bodies of the same thickness, are attainable.

To this end, the casting molds can be equipped with slightmodifications, such as closure devices for sealing the mold and afilling pipe, located above the level of the slip, that is provided witha closable air space for receiving the compressed air. The casting moldproduced by the novel method should be adjusted to a pore volume between30 and 60%. Casting molds of this kind can also be used as pressuremolds.

In order to replace or augment the compressed air, the casting mold canbe supported in a closed container and evacuated from outside.

The above-mentioned mold waiting times are applicable for stoneware orfor slip used for ceramic bathroom fixtures, for example. In the case ofporcelain slip, the filled waiting time and the mold waiting time areshortened considerably. The expenditures for the machine and the diecasting mold required by known die casting methods are hardlycomparable. By this method, not only solid and hollow casting, butcombined hollow and solid casting is possible.

A further provision according to the invention for the molding ofceramic compositions has to do with regulating the release of the moldedarticle from the plastic mold.

After repeated unmoldings, because of the increased water contentretained in the mold, the plaster mold tends to release the moldedarticle prematurely. This prevents the removal of moisture and increasesthe danger of shifting, especially of flat surfaces of the moldedarticle. The plastic molds used in accordance with the invention tendinstead to adhere to the molded article until dewatering is extensive.This can be accelerated by treating the body with warm air, and theinstant of the release of the body from the mold can be adjusted bymeans of temperature and interaction time. However, since this isassociated with possibly uneven drying beginning at the air-treatedside, attempts were made to accelerate the release of the body. Whilethe usual methods using lubricants such as talc, stearates and others,caused deposits to form and caused delayed body formation, a provisionaccording to the invention brought about an optimal result. Before theslip is introduced into the mold, it is briefly sprayed with a plasterspray. For doing so, the dihydrate is used in a 1 to 10% suspension. Thebody forming time is not changed in any way thereby, and the very slighttraces of plaster remaining on the molded article have no effect on itslater processing. If necessary, a small amount of lubricant can be addedto the mold separating spray.

Deposits and residues on the mold can be removed readily using warmwater and a conventional wetting agent.

The plaster suspension is prepared by mixing stucco plaster or modelingplaster in water (10% by weight); the mixture is stirred forapproximately 1 hour and is then ready to use. Combining the use of theseparating spray with a brief temperature treatment is advantageous inorder to release the body from the mold. The elevated temperature of thesolution can be produced by exposure to radiant heat or warm air. Forbodies from 3-5 mm thick, from 1-3 minutes of warm air at approximately50° C. suffices for separating them from the mold.

This method can also be used when the low-pressure process is used.After the body has been formed the mold is poured out and then placedunder pressure once again, using compressed air, and then heat-treatedto effect release from the mold. With these provisions, the drying timeof the body in the mold and hence the mold waiting time can be reducedto a few minutes. The heat treatment can be given to the body usingeither radiant heat or warm air. To release solid cast parts, the use ofthe above-mentioned separating spray is sufficient.

To produce porous mold parts for molding ceramic compositions, water andwater-emulsifiable, hardenable compounds are used as a water-in-oilemulsion. The pore volume is adjusted by means of the amount of water inthe emulsion. The pores must be predominantly open and must berefillable with water.

For use in pressureless casting, pore volumes between 45 and 60% arepreferred. The molds are not subjected to notable surface stress, andthe changes that occur with plaster, such as softening and degradationof the surface because of moisture, weak acids and alkalis andpolyphosphates have no influence, or only an extremely small influence,on the plastic molds.

Greater resistance to pressure and frictional wear are necessary whenthe molds are used as casting molds, turn molding molds and compressionmolding molds. By adjusting the emulsion to a low water content between20 and 45%, this is readily attained. The pore volume can also bereduced, and the mechanical strength increased, by means of fillers suchas microbeads of glass, barite, quartz powder and other fillers orpolymers in powder form. The permeability of the mold composition togases and liquids can be regulated thereby, in particular when wettingagents to be described below are added to the emulsion in a proportionof 0.05 to approximately 1%, with respect to the hardenable component.However, this may possibly impair body formation--which is indispensableeven in turn molding, compression molding and low-pressure methods.

Depending on the composition of the molds produced in accordance withthe invention and on the method used, such as pressureless casting,low-pressure casting process, turn molding and press molding, the moldsproduced in accordance with the invention attain a service life that isseveral times as long as that of plaster molds under the sameconditions. For instance, turn molds still do not exhibit any changes onthe surface after having been unmolded 500 times.

Compacting of the surfaces can, if desired, be obtained by applyingaqueous synthetic resin solutions, for instance withmelamine-carbamide-formaldehyde resins, epoxy resins or film-formingplastic dispersions.

The molds can also be thinned down in parts and combined with plastermold parts. The mold material can be worked, glued, coated, screwed,milled and turned like wood and reinforced with conventionally knownmaterials such as glass fibers, textile fibers and metal parts.

The method of making mold parts from water-in-oil emulsions, the oilphase of which are compounds capable of being being polymerized orhardened and of being emulsified in water, is known.

German Pat. No. 22 56 496, columns 2-8, describes the prerequisites andthe ingredients of hardenable or polymerizable water-in-oil emulsionsand describes how their proportions are adjusted, as well as referringto the changes brought about in the hardened product by adjusting thedegree of dispersion of an emulsion. To this end, emulsifiers thatresult in open-pored systems, as well as catalysts and accelerators arenamed, so the reader can be referred to this patent in this context,which is also reflected in other publications. The pertinent extractsfrom the literature will be summarized and listed hereinafter.

Although these methods were known, it had not heretofore been possibleto produce a plastic material that was suitable for the molding ofceramic materials.

More intensive tests of porous material samples produced by the knownmethod yielded results in terms of their behavior when coated with aporcelain slip that were therefore unexpected. Contrary to the idea thatthe hydrophobic plastics could not develop any capillary activity withrespect to aqueous media, there were a few samples that, similarly toplaster, within a few minutes formed a body that could be removed afterdrying. Conspicuously, the capillary activity with respect to water waslower, in these samples made from the same recipe, being approximately20% of the capillary suction of other samples, with an ascensioncapacity of 20 cm of a water column in 15 minutes on a profile standingupright in the water. However, these samples were not in a position toform a body. It was accordingly appropriate to assume that the capillaryactivity of a porous article, alone, is not decisive for body formation,but that the structure of the material also plays a role. The capacityof forming a body increased in those samples that were prepared with ahigher-viscosity emulsion and that had a highly predominant proportionof open pores in the total pore volume. Therefore, to generate a suctionthat is effective for body formation, the emulsion must be adjustedwithin a dispersion range that corresponds to the desired properties,yet is capable of varying depending on the type of polymerizable orhardenable liquids and possible additives contained in the oil phase.

In order to obtain reproducible results, the simplest criterion foradjusting the degree of dispersion of the emulsion is arrived at bydirectly using the body formation ascertained on a hardened profile. InExamples 1 and 2 and Table 3, the results of orientation tests show howbody formation varies as viscosity increases, in comparison withplaster.

This adjustment loses significance, however, if the already namedadditives that accelerate body formation are used. Apparently theseadditives are of critical significance in varying the fine texture ofthe material, which promotes body formation.

In order to produce the molds according to the invention, the followingexamples of hardenable components of the emulsion are advantageouslyused: Polyester resins (A) made from polybasic carbonic acids such asmaleic acid, fumaric acid, itaconic acid or their anhydrides, adipicacid, sebacic acid, phthalic acid, isophthalic and terephthalic acid andmultivalent alcohols such as ethylene glycol, 1,3-butylene glycol,1,2-propylene glycol, neopentyl glycol and similar diols. The resins aredissolved in monomers (B) suitable for cross-linking or mixedpolymerization. The resin in the solution is in a proportion of 40 to70% by weight.

Examples of monomers (B) are styrene, alphamethyl styrene, phthalic acidallyl esters, esters of methacrylic and acrylic acid (the latter as aplasticizer, for instance), but in particular styrene and methacrylicacid methylester.

Examples of catalysts (C 1) used are those soluble in monomers, such asbenzoyl peroxide, lauroyl peroxide, and also water-soluble peroxides,and as fast accelerators (D), dimethyl-p-toluidine and dimethyl ordiethylaniline are used. As the emulsifiers (E 1), water-in-oilemulsifiers are used; for producing open-pored products, polyolemulsifiers, block polymers of polypropylene and polyethylene oxidehaving at least 30% of hydrophilous groups in the total molecule andfrom 0.5 to approximately 3% by weight of the hardenable componentscontained in the emulsion have proved to be particularly suitable. Thewater-in-oil emulsifiers can be supplemented with small quantities ofdetergents (E 2) or surface-active substances, such as alkylarylsulfonates, fatty alcohol sulfates, fatty alcohol ethylene oxideaddition compounds and the like, which are known in the form ofcommercially available washing active substances. If powdered polymersor fillers are added, then the detergents for regulating thepermeability to gases and liquids can be used in small quantities of upto approximately 0.5% of the quantity of resin.

To accelerate the formation of a body (F), sodium disilicate anddisodium tetraborate, which are preferred as alkaline-reactive molecularwater-binding substances, have proved to be particularly suitable ascompared with other, less effective compounds such as the dihydrate ofcalcium sulfate. However, sodium disilicate and disodium tetraboraterequire different quantities of additives; it is recommended that theseadditives be limited to approximately 2 to approximately 12% by weight,in terms of the hardenable component of the emulsion. The substancesthat are usable for (F) can also be used in combination with oneanother.

An additional increase in the permeability to liquids and gases, butalso a reduction of the loss to polymerization, is effected withpowdered to fine-grained, moisture-expandable polymers (G) in thehardenable or polymerizable phase. Examples are powdered polymers, suchas polymerizates of unsaturated polyesters, 30 parts by weight, and 70parts by weight of a monomeric mixture of styrene and methacrylic acidmethylester 1:1, or a polymethylmethacrylate (bead polymerizate withfine grain size, grain diameter approximately 0.01 to 0.2 mm and amolecular weight over 250,000, which is also used in the examples).

Tap water (H) is used as the water.

The procedure according to the invention will now be described by way ofexample.

To the resin (A) dissolved in the monomers (B), emulsifiers (E 1, E 2),catalyst (C) or accelerator (D) and finally the additives for (F) and(G) are added and mixed in--the order can be changed--and then the wateris added, stirring slowly, and the water-in-oil emulsion is formed.Depending on the temperature and catalytic action, a solid mold part,which contains water, is obtained after approximately 15 to 120 minutes,the weight of which is reduced after drying by approximately theproportion of emulsion water, that is ±2-3%. The pore volume correspondsapproximately to the amount of water incorporated into the emulsion andis predominantly open (from 75-97% of the total pore volume).

                  TABLE 1                                                         ______________________________________                                        Specification of the Components                                               ______________________________________                                        A   Resin       unsaturated polyester of maleic acid and                                      glycols                                                       B   Monomers    B (1) styrene                                                                 B (2) methacrylic acid methyl ester                           C   Catalyst    benzoyl peroxide, 50% strength                                D   Accelerator n-dimethyl-p-toluidine, 10% strength                          E   Emulsifier  E (1) water-in-oil emulsifier of non-                                         ionogenic polyether glycols                                                   E (2) commercially available wetting agents                                   based on non-ionogenic tensides                               F   Additive for                                                                              F (1) disodium tetraborate                                        body formation                                                                            F (2) sodium disilicate                                       G   Powdered    fine-grained polymethylmethacrylate,                              polymerizate                                                                              molecular weight above 200,000, mean                                          grain size 20μ                                             H   Water       tap water                                                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Component Composition of the Examples                                         Parts = parts by weight                                                       Ex-                                                                           am-                                                                           ple  Components                                                               No.  A      B1     B2   C   D   E1  E2   F1  F2  G    H                       ______________________________________                                        1    52.0   48.0   --   2   1   2   --   --  --  --   100                     2    52.0   28.0   20.0 2   1   2   --   --  --  --   200                     3    52.0   28.0   20.0 2   1   2   --   3   --  --   100                     4    52.0   28.0   20.0 2   1   2   --   6   --  --   100                     5    52.0   28.0   20.0 2   1   2   --   8   --  --   100                     6    52.0   28.0   20.0 2   1   2   --   --  7.5 --   100                     7    52.0   28.0   20.0 2   1   2   --   6   6   --   100                     8    50.0   25.0   25.0 2   1   2   0.15 4   --  75.0 60.0                    9    50.0   25.0   25.0 2   1   2   0.15 4   --  50.0 75.0                    10   50.0   25.0   25.0 2   1   2   0.15 --  --  75.0 60.0                    11   50.0   25.0   25.0 2   1   2   0.15 --  --  50.0 75.0                    ______________________________________                                    

EXAMPLES 1 AND 2

The water component is stirred slowly with a paddle mixer (speed 300-400rpm) into the resin, dissolved in the monomers, which already containsthe emulsifier, accelerator or hardener in solution, and thewater-in-oil emulsion is formed. The viscosity increase as a function ofthe intensity and length of stirring. Samples are withdrawn after 1, 2and 5 minutes. In Example 1, the samples have a viscosity of 2500, 3700and 4200 cP; in Example 2, the figures are 1600, 2800 and 5000 cP. Afteradding and mixing in the appropriate hardeners, or appropriate quantityof accelerator, the samples are poured into small platforms, which are 9cm in diameter, to a depth of 12 mm and are cold hardened. Followingdrying and removal of the water of emulsion, the samples are damp-wiped,and a small amount of a porcelain slip (water content 32%) is appliedonto them. The slip spreads out to a layer thickness of approximately 2mm. In the samples, the time required until the surface became matte wasdetermined by stop watch. The same test was performed on a small plasterplatform (RG 1.05) for comparison.

The following results were obtained.

                  TABLE 3                                                         ______________________________________                                        Samples of Example 1                                                          Stirring time in seconds                                                                        60      120      300                                        Viscosity in cP   2500    3700     4200                                       Body formation in minutes                                                                       18       15      11                                         Sample of Example 2                                                           Stirring time in seconds                                                                        60      120      300                                        Viscosity in cP   1600    2800     5000                                       Body formation in minutes                                                                       28       18      6.5                                        Plaster                                                                       Body formation in minutes: 5.5                                                ______________________________________                                    

The body formation time is shortened with increasing viscosity. It onlybarely reaches the time with plaster in the case of Example 2, at 6.5minutes. The dependency between viscosity and body formation time isclear. The range of viscosity varies with the variation in thecomposition of the hardenable phase of the emulsifiers. The bodyformation on the plastic samples is shortened by up to 20% as the sliptemperature increases, at 40° to 50° C.

The simple orientation test demonstrates the behavior of the hardenedsamples of material in body formation and indicates under whichconditions and in what range of time the body formation takes place, andin what range of emulsion viscosity the particular body formationdesired is obtained.

The adjustment can be made largely reproducible via the components ofthe emulsion, as long as the temperature and stirring intensity areadhered to when the emulsion is prepared.

In the following examples, the formation and drying of the body areaccelerated by means of additives in the emulsion. It is notable thatthe above-demonstrated influence of the viscosity of the emulsion on thebody formation decreases markedly, in comparison with the effectobtained by adding the above-named additives. This is probably closelyassociated with the fineness with which the water is distributed in theemulsion, which is further increased if, as already mentioned, smallquantities of detergents are added. The hydrophilizing thereby producedat the same time appears to be of little significance.

In Examples 3-7, increasing amounts of additives suitable for bodyformation are added to the emulsion. They can be introduced along withthe resin or the water, or as a hot solution (60°-70° C.) or directlyinto the emulsion. Care must be taken that the emulsion, which reacts toadditives by increasing its viscosity, does not decompose as a result ofphase change. The emulsion is poured out onto platforms, and afterdrying, samples are tested for body formation. A plastic tube (forinstance, a PVC tube 6 cm in height and 4.5 cm in inside diameter) isplaced upon each sample. The tube is insulated with Vaseline and filledup with a slip having a water content of 25-30% and at a temperature of20° C.

After a filled waiting time of 30 and 60 minutes for the slip in themold, or 8 and 16 minutes in the case of porcelain slip, the liquidamount is poured off. After a further 10-20 minutes, the tube part isremoved; the body is further dried, then released and dried until itsweight remains constant at room temperature of 20° to 25° C. A controltest is performed in the same manner, using a small plaster platform ofsimilar design. The weight of the dry body is determined and comparedwith the body obtained on plaster, the latter being considered equal to100%.

In Table 4, the figures obtained for Examples 3-5 are shown,supplemented with figures for the material samples 206 and 208, whichwere obtained by the same recipe except with a smaller amount of waterin the emulsion.

The table clearly shows the considerable acceleration of body formation,which is also applicable to all ceramic materials. The body formationtime varies depending on the type of ceramic material, as is alreadyknown for molding with plaster.

The solidification of the bodies also takes less time than with plaster,in particular with body thicknesses of 6 to 8 mm, for example, or afterseveral successive unmoldings. The porous plastic mold removes up to 30%more water from the body as compared with plaster. The almost doublepore volume that is available in the mold, as compared with plaster, canbe fully exploited.

                                      TABLE 4                                     __________________________________________________________________________    BODY FORMATION IN COMPARISON WITH PLASTER                                     __________________________________________________________________________    Slip:                                                                         Bathroom-fixture ceramic                                                                          Fine fireclay Fireclay       Porcelain                    Dwell time:                                                                   30'          60'    30'    60'    30'    60'     8'     16'                   Dry weight,                                                                   g       %    g  %   g  %   g  %   g  %   g  %    g  %   g  %                  Plaster                                                                            22.1 = 100%                                                                           29.4 = 100%                                                                          18.9 = 100%                                                                          24.0 = 100%                                                                          22.5 + 100%                                                                          28.5 = 100%                                                                           10.3 + 100%                                                                          12.6                  __________________________________________________________________________                                                            = 100%                206          23.2                                                                             -21.1                                                                             15.8                                                                             -16.4                                                                             21.8                                                                              -9.1      23.3                                                                             -18.0                             208  22.2                                                                             ±0                                                                              28.8                                                                              -2.0                                                         304  23.9                                                                             +8.1 33.6                                                                             +14.3                                                                             18.7                                                                               -1.0                                                                            26.1                                                                              +8.7                                                                             23.8                                                                              +5.7                                                                             24.6                                                                             -13.6                                                                              12.6                                                                             +22.3                                                                             21.23                                                                            +36.3              306  27.6                                                                             +24.8                                                                              36.9                                                                             +25.9                                                                             22.0                                                                              +5.8                                                                             28.0                                                                             +16.6      29.2                                                                             +2.4 14.8                                                                             +44.0                                                                             20.0                                                                             +58.7              308  27.9                                                                             +26.2                                                                              39.5                                                                             +34.4                                                                             20.0                                                                             +16.4                                                                             30.8                                                                             +28.3                                                                             27.4                                                                             +21.3                                                                             38.5                                                                             ±0                             __________________________________________________________________________    The plastic samples used for comparison contained the following               proportions of hardenable component                                           in the emulsion used for preparation, in terms of 100 parts by weight:        Sample          Parts by weight of water                                                                  Parts by weight of body formation                 __________________________________________________________________________                                accelerator                                       206             50          6                                                 208             50          8                                                 304             100         3                                                 306             100         6                                                 308             100         8                                                 __________________________________________________________________________

The release of the body is delayed. The instant of release can beregulated, however, by brief heating at temperatures above 50° C. If theplastic mold is treated with plaster spray as mentioned above, then theplaster and plastic molds both release the body at the same time.

With the above experimental arrangement, up to 375 unmoldings wereperformed with one and the same plastic mold, without perceptiblechanges on the surface of the mold or of the body or in the function. Inthese texts, from 15 to 16 unmoldings were performed in succession atthe same location without interruption and with mold drying.

The formation of a body can also be accelerated by elevating thetemperature of the slip; this is known per se, however. While increasingthe temperature rapidly causes damage to the mold in the case of theplaster mold, the temperature of the slip can be raised withoutreservations to over 60° C., if desired, in the case of the plasticmold.

Experiments 8, 9, 10 and 11 are performed with the addition of a beadpolymerizate with and without using wetting agents. The proportion ofwater and hence the pore volume is thereby reduced, and the mechanicalstrength is increased. Body formation decreases by approximately half.The permeability to gases and water is markedly increased. Filter platesof the same thickness and the same amount of exposed surface area,produced in this way, exhibit twice the passage speed, for the samequantities of water at the same pressure. If the amount of wetting agentadded is increased further, then the permeability can rise up to10-fold; the body formation is equal to zero; the suction capacity issuperior only for water (ascension capacity of the water in 15 minutesis 15 cm); use for the method according to the invention is no longerpossible. Such products can be used for die casting when high pressuresof 10 to 50 bar are applied. Thus the applicability of the invention incontrast to known methods is clearly defined.

Possible materials for the apparatuses used to produce the porousplastic working molds are metals such as aluminum, zinc, low-meltingalloys (melting point between 120° and 200° C.), which may for instancealso be used for make molds in injection molding, and steel, but notnonferrous metals, as well as such plastics as polypropylene,polyethylene, epoxy resins and polyurethane casting resins.

In the following example, a recipe from Table 2 is used to manufacturecasting molds. In the list found in Table 4, for a bathroom-fixtureceramic composition, a favorable body formation in 30 minutes formaterial 306 is ascertained, which corresponds to Table 2, Example 4with 50% water and 6% body formation accelerator. According to thisrecipe, a casting mold having a mold wall thickness of 3.5 cm ismanufactured using an apparatus for a 0.5-liter pitcher. With this mold,the following comparison tests as compared with a plaster mold areperformed. The following data were ascertained:

    ______________________________________                                        Casting mold     Plaster     Plastic                                          Mold weight      3.8 kg      1.2 kg                                           Mold wall thickness                                                                            6 cm        3.5 cm                                           Type of slip     stoneware   stoneware                                        Liter weight     1.82        1.82                                             Slip temperature 26° C.                                                                             26° C.                                    Filled waiting time                                                                            75 min      15 min                                           Drying time in the mold                                                                        120 min     30 min                                           Drying temperature                                                                             35° C.                                                                             25° C.                                    Body thickness   5-6 mm      6 mm                                             Cycling time     195 min     45 min                                           Pours per day    2           6-8                                              ______________________________________                                    

The cycling time is shortened by 77% in the novel method, as comparedwith plaster. Similar results can also be attained with much largermolds, such as those in the area of bathroom fixtures, and with othertypes of slip, taking the thereby-dictated prolongation or shortening ofbody formation time, such as with porcelain, into consideration. Inaddition to the difference in weight, which plays a particularlyimportant role in transporting and storing the mold, entirely newperspectives are gained in terms of manufacturing considerations becausemultiple unmoldings per day are possible, and because of the longerservice life of the mold.

With the low-pressure method according to the invention, a considerableexpansion of ceramic molding technology is attained.

The above-mentioned three-part casting form (bottom and two side parts)is secured with two lashing straps surrounding the body of the castingmold, in order to perform the following experimental example. A fillpipe is mounted on the inlet, together with the rim of the inlet tightlyclosing the mold; in this test, the fill pipe communicates with acompressed-air line. See FIG. 2. The form is filled with slip, and thefill pipe is sealed off with pressure, using a small hydraulic press.Compressed air at 1 bar is supplied to the mold for 6 minutes. After 6minutes, the compressed air is evacuated and the mold is opened; theslip is poured out (naturally it can be aspirated instead, by insertinga suction tube into the mold), and the form is again put under pressureusing 2 to 3 bar compressed air; finally, the closed or opened mold isflushed with warm air at 50° C. for 2-3 minutes. After this, unmoldingcan be performed, and molding can begin anew. The molding cycle is thusreduced to 12 to 15 minutes. The additional application of pressurepartially replaces the suction capacity of the mold. It is thus possibleto perform a virtually arbitrary number of cycles in succession, withouttaking the pore volume into consideration. Since on the one hand thesurface of the mold is not stressed greatly, because of the low pressureapplied, and since on the other hand mold compositions having a low porevolume can also be used, because of the contribution of the pressure,the service life of the mold is impressive. Depending on the kind ofslip, from 300 to several thousand unmoldings can be performed. The lowapplication of pressure has still other advantages, however. Theoutfitting of the mold is virtually indistinguishable from a normalcasting form. The expense for machinery is reduced to a minimum. Theprocedure can be performed equally well in manual operation or with asmall automatic system. With a small rotary machine, a daily output ofup to 200 blanks can be attained, under the above-described conditions,using 6 casting molds.

The most important features of the invention for the molding of ceramicmaterials will now be summarized briefly, as follows:

1. For molding the ceramic materials, working forms for performingconventional processes such as casting, with and without pressure, assolid or hollow casting or combinations of the two, turn molding andcompression molding of bathroom fixtures, dishware, ornamental,structural and technical ceramics are used, which are produced using ahardenable emulsion comprising water and water-emulsifiable compounds.The mold parts obtained in this way have a predominantly open porevolume, which can be refilled with water and by the following provisionsbecomes capable of forming a body when in contact with ceramiccompositions:

(a) by adjusting the degree of dispersion of the emulsion;

(b) by means of additives which serve to accelerate and regulate bodyformation; and

(c) by adjusting the pore volume by means of the water content in theemulsion.

The provisions listed as (a) and (b) can each be used alone or they canbe used in combination. Provision (c) should be adapted to the intendedpurpose. As a minimum, the open pore volume should not be less than 10%of the total volume of the molding composition, while the upper limit ofthe total pore volume is approximately 60%.

2. The method also applies to provisions for considerably shortening themold waiting time, while largely protecting the mold,

(a) by using a low-pressure method, in which a low pressure of up toapproximately 3 bar is exerted on the slip, in the mold for the sake ofbody formation, until the desired body thickness has been attained;

(b) by exerting brief compressed-air pressure upon the now-formed body,up to approximately 5 bar, after the removal of the liquid component ofthe slip, in order to accelerate drying;

(c) by simultaneous, or subsequent, brief treatment with blown-in warmair, or by radiant heat, of the now-formed body until it separates fromthe mold.

These provisions can each be used alone or in combination in producinghollow cast parts, in order to shorten the mold waiting time.

3. The release of the now-formed body from the mold is

(a) shortened in time by treatment of the surface of the mold with aspray, which contains cemented plaster in suspension or plaster in theform of a dry powder; and

(b) additionally accelerated by briefly heating the body formed in thehollow casting.

The advantages of molding ceramic materials in accordance with theinvention are as follows:

The weight of the working molds is reduced to from 70 to 25% of that ofthe same mold made of plaster. The mold material can be worked similarlyto wood and thus offers novel possibilities and particularsimplifications in constructing and designing the molds.

The mold wall thicknesses should uniformly and generally be about halfthe thicknesses that are typical for plaster molds, and the mass of themold is thus decreased.

The filled waiting time and drying time of the body in the mold, incasting according to the method of the invention, amount to a fractionof the time normally required. The number of daily unmoldings aremultiplied, especially if the low-pressure die casting method describedis employed and if multiple molds or batteries of molds are used.

With the increased service life of the molds used for casting and turnmolding, considerable economies of material, space and otherexpenditures are attained.

I claim:
 1. A porous, open-pore, hardened, plastic composition suitableas a replacement for plaster for use as a mold in shaping a ceramicarticle by any of various ceramic shaping methods in which said mold hasceramic body formation properties similar to those of plaster by virtueof the capillary action of the open pores of said mold, said porous,open-pore, hardened, plastic composition having been prepared by forminga water-in-oil emulsion comprising an aqueous phase dispersed in acontinuous phase comprising (a) at least one unsaturated polyester resindissolved in at least one hardenable compound containing at least oneethylenically unsaturated group and (b) at least one emulsifying agent;incorporating in said water-in-oil emulsion about 2-12% by weight ofsaid hardenable compound of a material effective in accelerating theformation of a ceramic article to be shaped in said mold, said materialbeing selected from sodium disilicate and disodium tetraborate;controlling the aquoeus phase/oil phase ratio so that said porous,open-pore, hardend, plastic composition has an open-pore volume, whichis refillable with water, of about 10-60% of the total volume of saidporous, open-pore, hardened, plastic composition; and subjecting thehardenable compound of the continuous oil phase to hardening withoutbreaking the water-in-oil emulsion; and then drying to obtain saidporous, open-pore, hardened, plastic composition.
 2. A porous,open-pore, hardened, plastic composition according to claim 1 in whichabout 4-8% of said material is incorporated in said water-in-oilemulsion.
 3. A porous, open-pore, hardened, plastic compositionaccording to claim 1 in which the unsaturated polyester resin is madefrom (a) a polybasic carbonic acid or its anhydride selected frommaleic, fumaric adipic, sebacic, phthalic, isophthalic and terephthalic,and (b) a multivalent alcohol selected from ethylene glycol,1,3-butylene glycol, 1,2-propylene glycol and neopentyl glycol.
 4. Aporous, open-pore, hardened, plastic composition according to claim 1 inwhich the hardenable compound is selected from styrene, α-methylstyrene,phthalic acid allyl esters, and esters of methacrylic and acrylic acids.5. A porous, open-pore, hardened, plastic composition according to claim2 in which the polyester resin is made from maleic anhydride and glycoland the hardenable compound is a mixture of styrene and methylmethacrylate.
 6. A water-in-oil emulsion for forming a porous,open-pore, hardened, plastic composition suitable as a replacement forplaster for use as a mold in shaping a ceramic article by any of variousshaping methods in which said mold has ceramic body formation propertiessimilar to those of plaster by virtue of the capillary action of theopen pores of said mold, comprising (1) an aqueous phase dispersed in acontinuous oil phase comprising (a) at least one unsaturated polyesterresin dissolve in at least one hardenable compound containing at leastone ethylenically unsaturated group and (b) at least one emulsifyingagent; and (2) about 2-12% by weight of said hardenable compound of amaterial selected from sodium disilicate and disodium tetraborateeffective in accelerating the formation of a ceramic article to beshaped in said mold.
 7. A porous, open-pore, hardened, plasticcomposition prepared from the water-in-oil emulsion according to claim6.